The present invention relates to a drilling derrick and a method for erecting a drilling derrick on a fixed platform, a jackup platform or on a floating barge. More particularly the present invention relates to both the drilling derrick and method of erection that produces a derrick of significant strength and a capability of withstanding serious adverse weather, environmental or geologic conditions.
Drilling derricks are well known in the art and are very substantial structures that rise to a vertical height of at least about 150 feet up to a maximum of near 190 feet. Unlike the masts that are used for crane operation in oil field operations, drilling derricks are necessarily four-sided structures that must withstand the rigors of heavy winds and seas that include hurricanes and typhoons or earthquakes or other earth tremors that would topple far less sturdy structures. The drilling derrick must be erected on site because of its great weight and cannot be erected in a safe or quiet location and transported to the site. It has in the past been attempted to have masts constructed in sections and have the sections superposed one upon the other at the drill site but such proposals are not successful because with the height required for the drilling derrick, a crane must lift very heavy sections 100 to 150 feet above the drilling level or platform to effect the erection. Normally these platform cranes are small to medium size having significant reach and weight limitations and they are not tall enough to erect a derrick in one piece.
If a crane on a floating barge is to be used to attain the proper height, there is a great expense involved because the offshore platforms are often located from a few miles to several hundred miles offshore making the use of a very large barge crane impractical and extremely expensive.
The prospect of installing on the drilling platform a crane having the size and reach to be able to lift the drilling derrick even in sections is uneconomical for any platform owner to install such a huge crane capable of such erection of a drilling derrick in single or multiple lifts. This problem is particularly acute because drilling contractors typically drill a group of wells from a single platform and then move on to drill a group of wells on a different nearby platform so that every time the drilling rig--comprising: a drilling derrick; supporting structure; drilling machinery, etc.; used to drill a well bore for each well--must be moved from platform to platform. Thus the rig must be rigged up for a new location and then broken down to move by transport barge and a platform crane to a new location. The frequency of the rig up and transportation has made desirable some type of drilling derrick capable of being moved and yet capable of withstanding the serious adverse conditions of weather, environmental or geologic occurrences.
The current approach used by many drilling contractors is to erect the drilling derrick in a piece-by-piece method that enables the platform owner to achieve the desired drilling derrick structure of a rigid and serviceable drilling derrick. The problem, however, with this approach is it is labor intensive and usually takes from several days to at least several weeks to construct such a derrick in an piece-by-piece or stick-by-stick method.
Another problem is posed by safety regulations promulgated by the British and Norwegian governments that do not permit the stick-by-stick building of a drilling derrick requiring at times the rental of a huge semi-crane at a cost of several hundred thousand dollars per day. Even that possibility for erection of a drilling derrick is limited due to extreme weather conditions in many areas such as the North Sea where it is reasonably expected that an erection of a derrick could only be accomplished within a period of six to eight months a year. For these and other reasons experienced by those skilled in the art the problem of erecting a drilling derrick sufficient to meet the severe adverse conditions and to do so in an economical and safe manner has been a problem facing the oil and gas industry.